The present invention relates to a method and apparatus for recording data signals on a disk-shaped recording medium, and to a recording medium for recording data signals.
Hitherto provided is so-called xe2x80x9cmagnetically induced super resolution (MSR) technique.xe2x80x9d The MSR technique uses a material-characterized mask the behavior of which changes in accordance with the heat applied to the material. The changes in the behavior of the mask is utilized to record data at high density on a magneto-optical disk, thereby to reproduce images of super resolution, that is to reproduce images having high resolution that cannot be attained by optical reproduction technique.
A switched-connection, multi-layer film is used to provide an MSR magneto-optical disk. First, the principle of MSR will be explained, with reference to two types of two-layer magnetic films.
MSR achieved by means of FAD (Front Aperture Detection) will be described, with reference to FIG. 1.
FIG. 1 shows various directions in which the two-layer magnetic film formed on the recording surface of a magneto-optical disk may be magnetized. The magnetic film is composed of two layers 101 and 102. The first layer 101, or surface layer, is a reproducing layer. The second layer 102, or a base layer, is a recording layer. This holds true in any description that follows.
As shown at A in FIG. 1, the reproducing layer 101 and the recording layer 102 are magnetized in the direction opposite to the direction of an external magnetic field. As shown at B in FIG. 1, the reproducing layer 101 and the recording layer 102 are magnetized in the direction identical to the direction of an external magnetic field. Also shown in FIG. 1 is an interface magnetic wall 100 at which the magnetism of the reproducing layer 101 meets that of the recording layer 102.
As shown at A in FIG. 1, the direction of magnetization of the reproducing layer 101 is inverted when the temperature of the layer 101 rises from room temperature. That is, the direction is inverted when the intensity of the external magnetic field surpasses the sum of the coercive force and exchange force of there producing layer 101. When the temperature of the recording layer 101 falls to room temperature, the direction of magnetization of the layer 101 changes to become the same as the direction of magnetization of the recording layer 102.
As shown at B in FIG. 1, the direction of magnetization of the reproducing layer 101 remains unchanged even if the temperature of the layer 101 rises from room temperature. In other words, the direction is the same as the direction of magnetization of the recording layer 102.
MSR accomplished by RAD (Rear Aperture Detection) will be described, with reference to FIG. 2.
As shown at A in FIG. 2, the magnetic field of the reproducing layer 101 extends in the direction opposite to the direction of the external magnetic field, whereas the magnetic field of the recording layer 102 extends in the same direction as the direction of the external magnetic field. As shown at B in FIG. 2, both the reproducing layer 101 and the recording layer 102 are magnetized in the direction identical to the direction of the external magnetic field.
Namely, in the initial state, or at room temperature, the reproducing layer 101 is magnetized in a specific direction, irrespective of the direction of magnetization of the recording layer 102. When the temperature of the reproducing layer 101 rises from room temperature, the direction of magnetization of the reproducing layer 101 changes, becoming the same as that of the recording layer 102.
As shown at A in FIG. 2, the direction of magnetization of the reproducing layer 101 is inverted when the intensity of the external magnetic field surpasses the sum of the coercive force and exchange force of the layer 101. As shown at B in FIG. 2, the reproducing layer 101 remains magnetized as long as the sum of its coercive force and exchange force surpasses intensity of the external magnetic field.
It suffices to impart a proper intensity to the external magnetic field in order to maintain this relationship. Nonetheless, it is necessary to impart a large coercive force to the recording layer 102. Once the temperature of the reproducing layer 101 falls to room temperature, the reproducing layer 101 is magnetized in the same direction as the recording layer 102. Therefore, only the reproducing layer 101 is initialized and magnetized in the direction opposite to the direction of magnetization of the recording layer 102. Thus, one cycle of operation is terminated.
In summary, the reproducing layer 101 is magnetized in a certain direction when FAD shown in FIG. 1 is carried out. When the RAD shown in FIG. 2 is performed, the reproducing layer 101 is magnetized in the same direction as the recording layer 102.
Assume that the magnetized state of the recording layer 102 corresponds to a signal recorded on it. Then, in the process of reading data from the reproducing layer 101, a mark will disappear when FAD (FIG. 1) is effected and will appear when RAD (FIG. 2) is performed.
What is important is a temperature rise during the reproduction of data. The magneto-optical disk is rotating at all times. From this it can be understood that any part of the disk that follows the laser-beam spot formed on the disk will be heated to high temperature.
This fact may be taken into account when the magnetic layers are adjusted to cause the inversion shown in FIG. 1 and 2 at the high temperature to which that part of the disk has been heated. Then, two recording media illustrated in FIG. 3 may be designed.
Either recording medium shown in FIG. 3 comprises a reproducing layer 101, a recording layer 102 and a base layer 104. The base layer 104 has lands and grooves at the upper surface. The recording layer 102 is provided on the base layer 104, and the reproducing layer 101 is provided on the recording layer 102. Marks 112 at which signals are recorded are provided on each land.
As shown in FIG. 3, two marks 112 are irradiated with the laser-beam spot 113.
In FIG. 3, each dot indicates a mark that is appearing, or a part of the recording layer 102 which is seen through the reproducing layer 101 because the reproducing layer 101 is magnetized in the same direction as the recording layer 102.
Each circle shown in FIG. 3 indicates a mark that has disappeared, or a part of the recording layer 102 which is not seen through the reproducing layer 101 because the reproducing layer 101 is magnetized in a direction different from the direction in which the recording layer 102 is magnetized.
The magnetic layers may be adjusted such that a mark disappears at the high-temperature part as is shown at A in FIG. 3. In this case, the signal will be detected only at the part in front of the laser-beam spot 113. This manner of signal detection is therefore called xe2x80x9cFAD (Front Aperture Detection).xe2x80x9d
Conversely, the magnetic layers may be adjusted such that a mark appears at the high-temperature part as is shown at B in FIG. 3. If so, the signal will be detected only at the part at the rear of the laser-beam spot 113. This signal detection is therefore called xe2x80x9cRAD (Rear Aperture Detection).xe2x80x9d
Both FAD and RAD can detect a signal from only a part of the laser-beam spot 113. Advantage attained by using a pinhole can be achieved, whichever signal detection, FAD or RAD, is carried out.
MSR can be accomplished not only by FAD and RAD, but also by another method recently proposed. This is made possible thanks to the re-designing of the magnetic layers. The concept of the new method will be described, along with RAD and RAD, with reference to FIG. 4.
FIG. 4 shows thee lands 111. Marks 112, some seen and others not seen, are provided on each land 111. A laser-beam spot 113 moves on the land 111, toward the left. A high-temperature part 114 follows the laser-beam spot 113. In FIG. 4, too, each dot indicates a mark that is seen, and each circle represents a mark that is not seen.
FAD, wherein a mark preceding the laser-beam spot 113 is read, is illustrated at A in FIG. 4. RAD, wherein a mark following the laser-beam spot 113 is read, is depicted at B in FIG. 4. Shown at C in FIG. 4 is CAD (Central Aperture Detection), in which a mark is read at the center of the laser-beam spot 113.
CAD will be described in detail, with reference to FIG. 5. As shown at A in FIG. 5, with CAD it is possible to read a film at the center of the laser-beam spot 113 moving over the land 111. As seen from B in FIG. 5, that part of the land 111 that precedes the center of the spot 113 a little is at higher temperature than any other part.
As shown at C in FIG. 5, CAD is performed on a three-layer structure. The first layer is a reproducing layer 101, the second layer is a non-magnetic layer 102 made of AlN or the like, and the third layer is a recording layer 102. The reproducing layer 101 is magnetized in horizontal direction at room temperature. The recording layer 102 is magnetized in vertical direction. The non-magnetic layer 103 is interposed between the reproducing layer 101 and the recording layer 102.
Vertical magnetization anisotropy may surpass horizontal magnetization anisotropy in the reproducing layer 101 as the temperature of the disk rises. In this case, the data is transferred from the recording layer 102 to the reproducing layer 101 by virtue of magnetostatic coupling the non-magnetic layer 103 achieves.
No MO signals are detected from the reproducing layer 101 that is magnetized in horizontal direction. In CAD, data can be reproduced without using an external magnetic field. By contrast, an external magnetic field is indispensable to reproduce data in FAD and RAD.
CAD is advantageous in terms of reduction of track pitch. This is because CAD helps to increase resolution not only in the linear direction, but also in the direction of tracks.
In conventional recording media, the header section, which is the reference position for dividing the recording surface into sectors, is defined by pre-pits made in the recording surface. The recording density at the header section is inevitably limited by the wavelength of the light beam applied to the disk to read signals from the pits.
To enhance the recording density of the conventional recording media, the MSR technique is employed, in some cases, to record data in the data section of a medium, by using the header section defined by pre-pits, as the reference position for dividing the recording surface into sectors. It is demanded that the recording capacity of such a recording medium be increased so that the medium may record more and more data.
The present invention has been made in consideration of the foregoing. The object of the invention is to provide a method and apparatus for recording data on a disk at high density, thus increasing the recording capacity of the disk, and also a recording medium that can record data at high density and therefor has a large recording capacity.
To achieve the object, a data-recording method according is provided according to this invention. The method records data on a disk that has a data-recording surface having a data section in which units of data are to be recorded and a header section which is provided before the data section and serves as a reference position of the data section. The method comprises a step of recording data in the header section at such a high density that the data is reproduced with a super resolution.
A data-recording apparatus according to the invention records data on a disk that has a data-recording surface having a data section in which units of data are to be recorded and a header section which is provided before the data section serves as a reference position of the data section. The apparatus comprises means for recording data in the header section at such a high density that the data is reproduced with a super resolution.
A recording medium according to the present invention has a data-recording surface. The data-recording surface has a data section and a header section. Units of data are to be recorded in the data section. The header section is provided before the data section and serves as a reference position of the data section. Data is recorded in the header section at such a high density that the data is reproduced with a super resolution.
In the present invention, data is recorded in the header section of each sector at as high a density as in the data section, so that MSR reproduction may be accomplished. That is, data can be recorded in the header section at higher density than in the conventional recording medium, which has optical limitations. The invention can therefore provide a recording medium that has a large recording capacity.
Moreover, in this invention, only one header defined by pre-pits is formed in the surface of a recording medium, and any other headers are magnetically recorded on the recording medium. This enhances the recording density of the medium.
Since data is recorded on the recording medium at a density that accords with MSR reproduction and only one header defined by pre-pits is formed in the surface of the medium, the recording density can increase by 2% to 5% in the case of a 5.25-inch MO drive.
In the case where MSR is attained by FAD or RAD, a magnetic filed is applied in a data-erasing direction for the first identifier, and in a data-recording direction for the second identifier. Therefore, it is unnecessary to invert the direction of magnetic field to erase or record data from or in the data section. Nor is it necessary to invert the direction of magnetic field to reproduce the identifiers and the data from the data section. This helps to shorten the data-erasing time and the data-recording time.